<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="../js/jquery-1.11.3.js"></script>
    <script>


        $(function(){
            var lis = $('#nav2').css('color','red');
            console.log(lis);
        })

        document.getElementById('aa')//元素对象
        document.getElementsByTagName('li');// htmlCollectionOject [0,1,2 length]

        $('#nav2') //jQuery对象
        $('li');    // jQuery对象

    </script>
</head>
<body>
<li>aaa</li>
<li id="nav2">aaa2</li>
<h1>bbb</h1>
<p>ccccc</p>

</body>
</html>